In a competition, such as a downhill ski race, the speed of a competitor, such as a skier, can be measured nowadays by using, for example two photoelectric cells, which are placed a few meters away from each other. Such a speed measurement can also be made by means of a Doppler radar system, which uses a radar gun, such as those indicated on the website http://www.stalkerradar.com/sportsradar/. Several radar guns can be placed in proximity to the downhill course at various key points on said course.
Devices for measuring speed in a ski race, which may be stationary, are not capable of supplying speed continuously, but only at certain points on the race course. Moreover, no portable device includes means capable of transmitting the results in real time to a base station in order to display the speed live on a screen or on the television.
Conventional portable radar or ultrasonic devices also have the drawback that they can lose contact with a linked stationary speed measuring means during a downhill ski race. This means that even a wide-angle Doppler radar can lose sight of the ground during jumps in the race. This disrupts the real-time speed measurement.
US Patent Application 2002/0116147 A1 describes a portable device provided with a sensor unit connected to a controller. The sensors may be a speed sensor, such as a Doppler effect sensor, a power sensor, and a drop distance sensor, such as a pressure sensor or altimeter. An RF communication unit may be provided for communicating measurement data to a base station. Measurements from the sensors can be stored in the portable device and processed in said device prior to transmission.
However, such a portable device does not describe an activation and synchronisation operation at the start of the race, and an operation of calibrating the pressure sensor. It is not possible to accurately determine the speed, flight time and flight distance with a combination of the measurements made by the sensors, or to continuously transmit the speed measurement to a base station for display on a display screen, which are drawbacks.
EP Patent Application 1 406 066 A2 describes a device for determining distance in a race by measuring gradients and pressure differences. The pressure difference is measured by a pressure sensor, while the gradients are measured by an acceleration sensor, which takes account of static and dynamic acceleration.
The device also does not describe activation and synchronisation, or calibration of the sensors at the start of a race. No clear combination of the measurements made by the sensors is described for continuously accurately determining speed during the downhill ski race for transmission to a base station for display on a screen, which is a drawback.
US Patent Application 2002/0059044 A1 describes a portable device mainly for measuring a ski speed. To achieve this, a speed sensor and a sensor for determining jump or flight times are used. A microprocessor allows the information from the jump sensor to be converted to determine the flight time. A display device may be provided to show this time to the skier, but it is not possible to send information in real time.
Such a device does not describe activation and synchronisation, or calibration of the sensors at the start of the race. Further, no combination of the measurements from the sensors is described for continuously accurately determining the skier's speed for transmission to a base station for display on a screen, which is a drawback.
Other portable devices are known for measuring the speed of a skier. In particular, U.S. Pat. No. 4,546,650 can be cited, which describes a speed measuring device which includes at least one wheel in contact with the course and means for determining the rotational speed of the wheel. However, this type of device does not allow a precise and continuous speed measurement to be made.
EP Patent 1 084 422 B1 describes the use of at least one ultrasonic or micro-wave Doppler sensor, which is disposed on the ski, on the ski boot or on the belt of the skier. The Doppler sensor has a wide angle of aperture, which can vary to permit measurement with a precision of ±1%, but it does not allow a precise continuous speed measurement to be made from when the skier starts and during a jump on the course.
It is also to be noted that it is possible to envisage making a continuous speed measurement by using a GPS receiver. Depending on interference due to multiple signal paths, to the sky being blocked by mountains or other objects and to geometric dilution of precision, a precision of 95% can nonetheless be achieved. On a mountain slope with an inclination of 45°, horizontal speed is 30% lower than three-dimensional speed. In order to work accurately on a racing skier, the GPS receiver must be placed on the skier's helmet, but this represents an unacceptable safety risk during a downhill race. Further, as the sensor is not attached to the ski, there is a lack of precision due to movements between the head and the ski. Although GPS technology normally permits speed measurement in three directions, the user of the GPS device only receives two-dimensional speed horizontally. This may result in a big difference for the skier compared to his actual speed, which is a drawback.